1. Field of the Invention
The present invention relates to direct radiating array antennas, and in particular to a system and method for preferentially controlling the grating lobes of direct radiating array antennas.
2. Description of the Related Art
Direct radiating array (DRA) antennas are often used in satellite applications to transmit signals to terrestrially-based receivers. DRAs generally provide excellent performance and flexibility in terms of controlling the direction and magnitude of communication beams, but are typically both costly and heavy. A major contributor to the weight and cost of DRAs is the large number of elements that are used in the array. Such elements can number in the thousands, especially for high frequency, high gain applications. For a given aperture array size, the number of elements is inversely proportional to the square of the element spacing.
The main lobe of a DRA pattern is formed in a direction where the waves emanating from all of the DRA elements are approximately in phase. Communication beams from the DRA are therefore controlled by controlling the phase relationship of the signals emanating from the elements. Additional and generally undesirable major lobes, known as “grating lobes” can form in directions where the waves radiating from the adjacent rows of elements are out of phase by multiples of 360 degrees (or a full wavelength).
In many practical cases, the element spacing, and hence the number of elements, is driven by the desire to keep the energy emanating from the grating lobes from falling upon the Earth and potentially causing interference with other communications.
What is needed is a DRA that has an increased element size while maintaining acceptable grating lobe performance, and keeping the aperture utilization efficiently (the ratio of the aggregate radiating elements area to the available aperture area) substantially unchanged. The present invention satisfies that need.